Some network protocols claim to be mesh networks simply because their nodes can talk to one another. This article in our technical discussion on the WirelessHART protocol discusses the features of true mesh network like WirelessHART versus “fake” mesh networks.
What makes a network mesh?
There are three properties a network must have in order to be a true mesh network
- First, every node must be able to talk to its peers. That is, each node has the same functionality from the perspective of network topology. In a true mesh network, no node serves exclusively as a router or hub.
- Second, multiple paths must exist for a packet to get to its destination. This includes multiple paths to and from the gateway.
- Third, the paths cannot be simply a matter of changing directions, as in a ring. While a ring provides multiple paths (two), the two paths differ only in the direction the packet moves through the ring.
Many networks claiming to be mesh networks are actually tree networks, such as Zigbee RFD. Tree networks have many branches, but only one path from source to destination.
Remember the “good old days” when the only form of distance communication was stationary, land lines? (If not, talk to someone over 30.) When you needed to get a message to someone, you dialed their number. If the line was busy, you had to wait. There were no other options.
Fast-forward to the present where cell phones, e-mail, text messages, voice mail, and tweeting are all available. Can’t get someone on the phone? Send leave a voice mail. If it’s urgent, send an e-mail, text message, or tweet. There are multiple paths available to reach your destination.
The availability of multiple paths provides a real advantage to mesh networks. It keeps you (or a node in the network) connected even if one path breaks down. Even if your cell phone dies, you can still have access to e-mail. If a node in the network goes down, another path can be found through a different node.
Multiple paths in a mesh network also provide more timely contact. A caller can leave a voice mail or send a text message if you are engaged in a conversation. In the old days, they just had to keep trying until they could get through. Tree networks are like that. But a mesh network gets the message through.
Mesh networks like WirelessHART are a true improvement over single path networks.From a network point of view, the “good old days” aren’t so good.